This is a mandatory worship for islamic religion. Muslims sacrifice a sheep or a cow generally every year. But it has not to be every year.
In fact, the prophet made this worship only once in his life and only when he hes gone to hajj. In other say this is a mandatory worship for hajjies. But, because of there is an order in quran as "sacrifice an animal (for me)", muslims try to do it in every year, weather they in hajj or not.
But I'm not sacrificing an animal this year. I think it is more correct to do it at least, because the prophet did this worship only once. this is my personal opinion that most of the hodjas think that an animal must be sacrificed every year. but I am skeptical about this recommendation because they are the problem of intelligence. It is clear that prophet made it only once in life so that every year sacrificing it is not necessary. I'm sacrificing it not every year but some years when I feel myself good. But I recommend you listen to hodjas, but not be, because they are crowdy.
Greetings the muslim world in feast of sacrifice.